Although diminishing muscle strength in older adults has been shown to be associated with functional decline and disability, muscle power declines earlier and at a faster rate. It has been suggested that loss of lower extremity muscle power may be more important than loss of muscle strength, especially with regard to limiting certain activities of daily living (e.g., walking, rising from a chair, ascending or descending stairs). In addition (1) muscle power, as opposed to muscle strength, represents a critical variable in situations where postural stability is challenged(e.g., a trip/slip) and (2) women are more at risk for disability and have lower muscle power, when controlling for body mass. Despite the importance of declining muscle power, there is limited information about its association with physical function and disability. Our proposed exploratory secondary analysis will focus on mobility disability, which plays a key role in the independence of older adults. In examining mobility disability, we will explore whether or not there is a curvilinear (i.e., nonlinear) relationship between muscle power and physical function, which could indicate that a threshold may exist for muscle power. This association has been suggested for strength and physical function. Therefore, the primary aim of this project is: 1. To estimate in older adults (using InChianti data) the differences in mobility disability that are associated with differences in lower extremity muscle power and muscle strength, for purposes of planning future studies. The secondary aims of this study are: 1. To explore the relationships between lower leg muscle mass, muscle strength, functional performance (walking, balance, chair rises), and self-reported mobility disability and covariates such as age, gender, education, depression, comorbid conditions, body mass and height. 2. To explore cross-sectionally whether the relationship between lower extremity muscle power and mobility disability is curvilinear (non-linear). 3. To explore whether the lower leg muscle cross-sectional area is associated with muscle power.